Mesoscale Discussion 178

Issued

Feb 14, 2017, 3:57 AM CST (09:57 UTC)

Expired

Feb 14, 2017, 6:30 AM CST

In force

3 hr

Issued by

the Storm Prediction Center

Chance of a watch

60%

The Austin/San Antonio radar (KEWX), 109 km from the middle of the area, began a volume at 09:57 UTC, the scan nearest the moment this went out.

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• Tornado Watch 32Feb 14, 5:05 AM CST

884 
ACUS11 KWNS 140957
SWOMCD
SPC MCD 140957 
TXZ000-141230-

Mesoscale Discussion 0178
NWS Storm Prediction Center Norman OK
0357 AM CST Tue Feb 14 2017

Areas affected...South-central and Southeast Texas

Concerning...Severe potential...Watch possible 

Valid 140957Z - 141230Z

Probability of Watch Issuance...60 percent

SUMMARY...A severe threat is likely to develop across south-central
Texas over the next hour or two. A tornado threat along with
isolated large hail and wind damage will be possible as a linear
convective system organizes and moves from eastern parts of the
Texas Hill Country eastward into southeast Texas this morning.
Weather watch issuance will need to be considered once the exact
corridor with the greatest severe threat becomes apparent.

DISCUSSION...The latest surface analysis shows a cold front
extending southward from the Dallas/Fort Worth Metro along and just
east of the I-35 corridor to near Austin where a mesolow is
analyzed. The front extends southwestward from this surface low to
near San Antonio where a second surface low is analyzed. A warm
front extends eastward from this surface low into the Houston area
with surface dewpoints south of the front across the Texas Coastal
Plains mainly in the 65 to 70 F range. 

In addition, water-vapor imagery shows an upper-level trough
approaching the lower Rio Grande Valley. Increasing large-scale
ascent ahead of the shortwave trough along with lift associated with
a developing low-level jet in south Texas will likely result in a
gradual expansion of thunderstorm activity across south-central
Texas over the next couple of hours. RAP forecast soundings near and
to the south of San Antonio early this morning gradually weaken a
capping inversion near 700 mb which will make conditions
increasingly favorable for surface-based development. The latest
HRRR forecast suggests that surface-based storms will first initiate
along the cold front to the south of San Antonio with this
convection expanding northward and organizing into a line. MLCAPE
estimated to be from 1000 to 1200 J/kg along with 40 to 50 kt of 0-6
km shear will support supercell development with the stronger cells
embedded in the line. Storm relative helicities of 300 to 325 m2/s2
evident on forecast soundings will be sufficient for a tornado
threat associated with supercells. The line of storms is forecast to
move eastward into the Houston area by late morning where a threat
for tornadoes, wind damage and hail will be possible.

..Broyles/Edwards.. 02/14/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...HGX...CRP...EWX...

LAT...LON   29179893 28099882 28099802 28639609 29139502 29509496
            29899528 29959661 29729844 29179893

Mesoscale Discussions in Texas, 2017Every mesoscale discussion in 2017

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.